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Management of pregnancy should include level II sonographic examination, high-resolution karyotype, and molecular testing for NSD1 and GPC3 mutations. If these tests are negative, imprinting disorders of 11p15.5 should be tested.

Newborn treatment should include medical genetics consultation, cardiac evaluation, and monitoring for hypoglycemia.

Some of the overgrowth conditions are associated with a predisposition to childhood cancer.

Several of the overgrowth conditions have Mendelian patterns of inheritance.

CONDITION

The overgrowth syndromes refer to a heterogeneous group of conditions characterized by generalized excessive growth for gestational age. Many overgrowth syndromes are associated with anomalies, developmental delay, and a propensity for tumor development. Diagnostic characterization has been difficult because of the overlapping clinical features in many of these syndromes (Cytrynbaum et al., 2005). Recent studies using high-resolution cytogenetic techniques, as well as molecular analysis of several genes, have illustrated the fact that there is substantial clinical as well as molecular overlap amongst the overgrowth disorders (Baujat et al., 2005).

INCIDENCE

The overall incidence of fetal overgrowth is unknown but it is not rare. The incidence of Beckwith–Wiedemann syndrome is about 1 in 13,700 livebirths (Cytrynbaum et al., 2005). Beckwith–Wiedemann syndrome is more common in women who have undergone in vitro fertilization to conceive. It is estimated that Beckwith–Wiedemann syndrome occurs in 1 in 4000 deliveries to women who have used assisted reproductive technology. Another common condition associated with fetal overgrowth is Sotos syndrome, which has an incidence of 1 of 15,000 livebirths (Tatton-Brown and Rahman, 2007). The incidence of some of the other rare genetic conditions, suchas Simpson-Golabi-Behmelsyndrome (SGBS), is unknown.

SONOGRAPHIC FINDINGS

In the obstetric literature, there has been no prospective study performed to ascertain the outcome of fetuses documented to have overgrowth. There have, however, been reports of prenatal ultrasound findings in fetuses that were postnatally diagnosed as having a specific syndrome. For example, Reish et al. (2002) described three unrelated cases of Beckwith–Wiedemann syndrome and tabulated anomalies that were detected prenatally. The anomalies common to all of the fetuses included overgrowth, polyhydramnios, placentomegaly, macroglossia, and a distended abdomen. In addition, Le Caignec et al., (2004) described a case of Beckwith–Wiedemann syndrome in a 28-year-old G3P1-pregnant woman who underwent sonography at 28 weeks of gestation. The fetus was macrosomic, but also had bilateral enlarged echogenic kidneys with a loss of corticomedullary differentiation.